Pad



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PAD

Filed July 2. 1953 United States Patent O PAD William H. Ashton,Philadelphia, Pa., and Joseph N.l

Masci, Metuchen, N. J., assignors to Johnson & Johnson, a corporation ofNew Jersey This invention relates to foot produtcs in the form of a pad,such as com pads, which are intended to relieve localized Apressures onthe foot and ,thereby relieve irrita- "tion.

Many types of felt pads are used in the care of the foot. The functionof pads is either to relieve pressure or to obtain support. They areused under the longitudinal and metatarsal arches for support and asrelief or curvative aids in the healing of corns, bunions, bunionettesand other growths. The pads can be either permanently or temporarilyapplied to the interior of the shoe, or they can be secured to the footin the right place. The pads are generally anchored in place in the shoeor on the foot by means of a suitable adhesive especially designed tomeet the needs and perform the desired function.

Felt corn and bunion pads are presently available on the generalconsumer market. They are anchored to the site by either apressure-sensitive or remoistenable adhesive. The pads are died out oftlat felt stock resulting in square corners between the top surface ofthe pad and the side surface. They are usually round or oval.

Chiropodists, orthopedic surgeons, and their associates, do notgenerally use the conventional round or oval pad having vertical edges.This is because the edge is too hard or the prole wrong for theirtherapy. These specialists have found that conventional consumer feltpads can cause rather than relieve pressure irritation. Hence, it hasbeen the practice for physicians to prepare specially their own pads soas to translate the pressure of the shoe away from the corn or bunionarea. This has been achieved by bufling or cutting the thick felt toproduce a skived or tapered edge. The tapered edge may also be obtainedby building up the article from thin layersv laminated together. Theprocess used has been a hand operation in every case and has beentedious, expensive, and limited to use by skilled persons. Further,although certain partial relief has been obtained by use of theskived-edge corn pads, this relief has not been to the extent desiredand the need has been felt to obtain still further dissemination anddecentralization of localized stresses on the foot in the area ofirritation.

One object of the invention is to produce felt pads which afford greaterdecentralization and spreading of stresses away from localized spots ofirritationas compared with prior art pads.

Another object of the invention is to provide a valuable economicalprocess for producing a pad having skived or tapered edges.

A further object is to devise a process adaptable to a l high degree ofautomaticity. A still further object is to produce pads, preferably footpads, having a very high degree of resiliency.

The products of the present invnetion are pressurerelieving pads adaptedto be used adjacent the human body, the pads having tapered edges. Thepads are formed from a mat or felt of certain fibers of textile lengthdescribed more fully below. The invention pads have the additional andessential property that the density of '27,854,974 Patented Oct. 7, 1958ICC is greater at the tapered edges than at thicker central ponA tionsof the pad.

In manufacture of corn pads and other pressure-relieving pads adapted tobe used adjacent the body, the qual* ities of resiliency, elasticity andabrasion resistance are quite important. Pads made of felt must becomposed of fibers whichinherently have the right combination of theseproperties. According to the invention, the requisites of leesiliency,elasticity and abrasion resistance are ful- The invention may beconveniently understood by reference to the attached drawing in whichthe reference numbers designate corresponding parts in the severalfigures.

Fig. 1 is an isometric view of an oval shaped corn pad.

Fig. 2 is a sectional view of a portion of a pad taken along plane 2 2of Fig. l, the plane being perpendicular to the bottom surface of thepad.

Fig. 3 is a sectional view similar to Fig. 2 of a prior art corn pad.

Fig. 4 is also a sectional view similar to Fig. 2 of another product ofthe invention. f

Fig. 5 is a view illustrating molding of the invention pad, the drawingshowing only the portion of the pad and mold corresponding with thesection 2-2 of Fig. 1.

Fig. 6 shows a section of another type prior art corn pad.

Reference number 10 designates the body of a corn pad generallycircular, e. g. oval shape, and having adhesive mass 11 applied to. itsbottom at surface 12. Pad 10 has a vertical internal edge 15, a shortvertical outside edge 16, and a sloping or skived top surface 17.

ln Fig. 4 the invention com pad is shown as having a slightly modifiedcross scetion, that is, instead of the triangular cross section, thecorn pad is provided with an oval shaped top surface. In the Fig. 4 padboth internal vertical surface 21 and extemai vertical surface 22 aresmall and of approximately the same dimensions. Adhesive mass on thebottom surface 25 is shown at 26.

The notable characteristic of the invention brous pads is that the edgeportions 30 in both the trapezoidal and the rounded top pads havegreater fiber density than the central portions 31. Generally, thisliber density varies inversely as the thickness t of the pad at anypoint, i. e. the smaller edge thickness t to the larger centralthickness t'." This increased ber density near the edge portions of thepad is important in the pad function since it has less compressibilityand hence greater resistance to compressive stresses as will be morefully explained below. Referring to Fig. 5, there are shown a fixedsupport 35 and a continuous web of batting or felt material 36 which isthe material of which the invention pads are made. Web 36 is made ofstaple fibers of synthetic polymer described above and has substantiallyuniform weight per unit area.- Mold or plunger 37 has the shape of thetop rounded surface20 of the pad shown in Fig. 4. Means not shown areprovided for heating mold 37 and support 35 to the temperature levelrequired to cause permanent setting of ,the fibers in the web.lPreferably web 36, before it arrives at the point where mold 37 islowered, is moistened to a predetermined water content sufficient toprovide the amount of steam which will facilitate molding of the webwhen the heated member 37 is lowered onto the heated support 35. Thelower edge portions of mold cavity surface 38 compress correspondingparts of web 36 more than the higher central portions of the cavitysurface. Since the web has a unform weight per unit area, the morehighly compressed parts of the web will have a higher unit density. Theheat causes the fibers to set in the shape of the mold. After themolding operation, plunger 37 is raised and web 36 moved along thedieing out operations not shown in registry with the molding operationYdesigned to produce a corn pad having a cross section as shown in Fig. 4and a central opening as shown in Fig. l. Molds of corresponding shapeare utilized for preparation of .nids having cross section shown in Fig.2, and of course rrious other shapes may be made according to need withsuitably designed molds.

The advantages of the invention corn pad become particularly apparentfrom consideration of the forces to which the pad is subjected in use.The skived or tapered pads heretofore made by cutting or abrading p'dshaving rectangular-cross sections are illustrated in Fig. 6. Vectorarrows D andD indicate schematically the direction and magnitude offorce which results against member 45 when it is pushed against the padin use by force 45. It is seen that the amount of force on oppositeedges of the bottom surface of the pad (adjacent the body) are aboutequal and are inclined at an angle to the vertical. The equality of theforces is obtained partly by reason of the conformity of the pad to theshoe and the foot of the wearer. Furtherthe ber density at the left sideof the pad is the same as the ber density at the right side of the pad.Therefore, the left side will not tend to bear any more of the totalforce than the right side, and the right side may even bear a greaterproportion due to the tendency of the high point of the pad in this zoneto resist selectively any incidental force applied directly vertically.Whatever advantages may have been obtained by reason of skiving theedges as shown in Fig. 6. it would be desirable to increase theproportion of the total stress D borne by the outside edge of the pad,as compared with the stress D' borne by the intemal portion of the pad.

Referring to Fig. 2, the plane 40 represents the surface of the shoe orother object applying force to the body, and the arrow 40' representsthe magnitude and direction of application of the force which bearsdirectly against upper surface 17 of pad 10. Vector arrows A and-Arepresent the direction and magnitude of resistance force to force 40'at the outside and inside margins of the pad, respectively. Force 40'tends to compres'- the fibers in pad 10, and the fibers resist thiscompression. However, the ber density is graded from high density atzone 30 of the left side of the pad, to lower density in zone 31 of theright side of the pad. In zone 30 the bers, being already compressed,resist more strongly than does zone 31 further compression. Hence, it isseen that force A is substantially greater than A which indicates thatthe stress or resistance force borne by the pad is disseminated anddispersed from the sensitive area being protected which is near thecenter of the pad, that is, near vector force A'.

ln Fig. 4 the force is applied to upper surface 20 of thc pad from aninclined plane 50, as showz. Here the resistance force B from the edgeof the pad 30 is shown by the direction and length of the vector arrow,while the resistance force B' at the center of the pad is also shown bythe other vector arrow. Due to the greater density of the pad at point30, this portion tends to share more than its normally proportionatepart of the total force 50', and hence arrow B is longer than arrow B',indicating a shift of force and stress away from the more sensitiveareas of the body being protected at the right side of the drawing.

In Fig. 3 we have a conventional type corn pad having a square crosssection. The force here 55' is applied A from a horizontal surface 55bearing directly against upper surface 56. Resistance forces C and C'are equal since the ber density of the pad is the same at the right andleft ends of the pad. The square cross section pad, of course, suersfrom the objection of nonconformity which the skived pad is designed tocure. Further,

no shifting of stress to the left, away from the sensitive area of thebody being protected, has been obtained.

To provide the stress-relieving properties of the invention padding asdescribed above, the ber density of the 5 edge portions of the padshould be substantially greater than that of center portions. Generallythe ratio of the ber density, edge to central, will be at least about2:1, preferably at least 5:1. When pads are made by compressing a sheetof uniform weight, the thickness ratio, i. e. the ratio of edgethickness1" to central thickness r'," will be the-inverse of the density ratio,since the pad, according to the procedure described above, is made bycompressing such sheet to diterent degrees at different points therebyto produce'the diterent densities. However, the density is not limitedto this inverse ratio fea-v ture since it is possible to obtain theadvantageous high density edge feature of the invention by othermethods. i

Materials which are particularly suitable for invention pads are.certain synthetic polymers, these being polymers (including copolymers)of acrylonitrile, polymers (including copolymers) of polyethylene, andpolyesters of polyhydric alcoholsand polybasic acids, specically,polyethylene glycol-terephthalic acid esters and their derivatives.Polyacrylonitrile Ais made and sold under the trademark Orlon, andpolyethylene glycol terephthalate is made and sold under the trademarkDaeron Fibers of these polymers have beenfound to have inherently theresiliency,l elasticity and abrasion 'resistance desired for bodyprotective pads, and hence can be used alone without incorporation ofsuch conventional corn pad bers` as wool.

The molecular weight of the polymer in each case should be suicientlyhigh to provide a ber having a melting point high enough to suit therequirements at hand. The melting point of the polyester ber may beabout 480 F.; the temperature at which the polyacrylonitrile begins tostick, about 455' F.; and the melting point of the polyethylene, about230-250 F. The bers are stretched during manufacture so that they haveintemal stressesA which when the bers are heated above a certain settingtemperature will be relieved resultingin change of shape, usuallyshrinking of the bers. The polymer bers become entangled with oneanother and adjacent bers and hence shape is retained permanently by themolded pad. Whatever may be the mechanism of the action taking place inthe heating operation, the bers take a permanent shape, and the shape ofthe products made up by the bers may be 'controlled by the amount ofpressure and the shape of the mold used for the heat-setting operation.The bers in the pad of the present invention have been previously set bymolding to the desired tapered shape and the internal stresses relievedso that the pads remain permanently tapered or skived. 'The pads arepreferably subjected -to heat and pressure as described above, suitablyalthough not necessarily in direct contact with steam, at temperatureswithin the range 180 F. to 250 F. The temperature at which heat settingand strain relaxation take place will determine the temperature to-whichthe material may tllilreafter be heated without suering any change in spe.

The bers prescribed can be used alone, in combination with one another,or in combination one or more with wool, cotton, cellulose or otherller. In the felt products of the invention many combinations andarrangements of ber content are possible. Due to the greater abrasionresistance, loftiness and resilience of the polymer bers describedabove, wider limits are possible depending upon the properties desiredin the n- 70 ished article. Generally, however, felts or battings havinga thickness in the approximate range 0.05 to 0.25 inch, and a weight inthe range 2.0 to 64 ounces per square yard are suitable. The felt orbatting in order to be suitable for the invention products from thestand- 75 point of resiliency as indicated below should have 'the 5polymer bers described above present in content within the range 50% to100%, and any ller ber should be present in an amount not more lthan50%.

As stated above, in the manufacture of a body protective pad, berresiliency is of great importance. The resiliency, in order to aordproper cushioning effect and resistance to stretch .should be in theapproximate range 70-l00%. Resiliency is measured on a metermanufactured by Federal Products Corporation, Model 59E-11, having adial micrometer with 1,4000 readings and circular presser foo* area of lsquare inch (1.129" diameter). Before test the felt is conditioned forat least l24 hours at 70 F. and 65% relative liumidity. Approximately 2inches square are cut from the felt, and the determinations are carriedout in a constant temperature room. The initial thickness, T0, ismeasured with a ten ounce load applied for ten seconds by theinstrument. Then an additional 1.5 pounds are added 'to the ten `ounceload for one minute, and the reading T, is taken. After the one minuteload period the total weight (l oz. plus 1.5 lbs.) is removed and thesample allowed to recover its initial thickness for a period of oneminute. Then the nal thickness T1 is measured using the l0 oz. load for10 seconds. Resiliency is taken as T1 minus Ts. Percent resiliency istaken as 1,D Txioo Three dete:minations are made for each sample, andthe results averaged for each of initial thickness and percentresiliency.

Standard'individual lament deniers of the bers of the invention aresatisfactory and are of the order of 0.5 to 3 denier. Felts used tofabricate pads anchored to the foot fall into the low range of ouncesper square yard, e. g. 2.0 to 24.0, whereas those used under the foot,on the shoe, or on other parts of the body, tend to fall in the higherrange of about 20 to 64 ounces per square yard. Thicker pads, of course,may be utilized for applications on other parts of the body. Aformulation-having particularly suitable properties in the manufactureof corn pads consists of '50% polyacrylonitn'le ber, 50% polyester ofterephthalic acid and ethylene `glycol, the felt having a weight of 20ounces per square yard and a thickness of 0.18 inch.

The preferred bers described above have heat-set binding properties,that is, they hold together adjacent fibers by entwining themselvesaround or entangling with such adjacent bers, thereby exerting a chaintype holding action. According to a modification of the invention, bersare employed which bind by virtue of their coalescent propertiesactivated by heat, which is another type of heat-setting; for example,vinyl chloridevinyl acetate copolymer (8S-l5), polyvinylidine chloride,ethyl cellulose or cellulose acetate bers, may be blended with bers ofwool or other felt-forming material. Blending of the felt-forming ber isnecessary to impart the desired resiliency, elasticity, and abrasionresistance. The felt is molded under pressure and high temperature toactivate the binder bers by softening and causing them to adhere toadjacent bers, and thereby retain the felt in its compressed condition,i. e. with edge portions having greater density than central portions asspecified above. Generally the limits of coalescent bonding ber contentwill be substantially lower than the minimum 50% content ofpolyacrylonitrile, polyethylene and polyester stated specically above,i. e. approximately 25%.

Another modification suitable for producing the protective pads of theinvention having denser marginal' boxymethyl cellulose, or urea ormelamine-formaldehyde resin, impregnated onto the felt bers. In eachcase the pad is molded with heat into its nal shape at which time theadhesive properties of the binder become effective and retain the padpermanently in the desired shape.

One suitable process having a high degree of adaptability to automaticoperation has the following stations: (l) feeding; (2) wetting; (3)molding; (4) application of adhesive mass; and (5) dieing. The felt,suitably of the entangling bonding ber type, is fed into the unit onlong rolls of the proper width. It is then wetted with water spray orwith water vapor. The wetted felt is then drawn into the molding stationdescribed above which is heated to temperature above 212 F. and is ofthe continuous multiple type unit molding equipment. This station setsthe felt to the shape of the mold by applying a pressure of 500 poundsper square inch, relieving the strains as described above, and the heatis so regulated that the molded forms leave the station substantiallydry. The continuous molded sheet then passes to the adhesive stationwhere either pressure-sensitive adhesive mass or remoistenable glue isapplied. This sets immediately and the sheets are died out under theproper registration with the molded forms to eject the molded articles.The molding pressure is controlled to produce (from the 0.18 in. thick,20 oz. felt described above) a pad having an edge thickness of 0.031 in.and a maximum thickness in central portions of 0.125 in. The local berdensity at such edges is 0.48 oz. per cubic inch, while the local berdensity at the central portions is 0.12 oz. per cubic inch.

For a batch operation a plate mold was prepared with four recess unitshaving dimensions approximating a standard round corn pad but withtapered edges as illustrated in Fig. 4.' A felt made of 100% bers ofpolyester of ethylene glycol terephthalic acid (Dacron), the bers being3 denier, the felt having a thickness of 0.134 inch and weighing 19.2ounces per square yard, was placed on the plate mold and covered with apiece of x 80 cloth containing about 300% water. The device was placedin a press the top plate of which was at a temperature of about 300 F.The press was closed until the gage pressure was 8000 pounds and heldthus for l5 seconds. The pressure was then released and the moldedlsheet removed from the plate. Individual com pad shapes are found to bepermanently molded in the at sheet. These forms were died out to producecorn pads of form having a cross section illustrated in Fig. 4.

The process stations may be combined where practicable, or their orderaltered when necessary. For example, the wetting can be combined withthe molding station and the molded sheet died out and adhesive appliedto the individual pads. The adhesive station can be altered in variousways depending on the type of mass and anchorage desired. The moldedsheet stock may be passed through an operation which calenders apressure-sensitive adhesive onto the sheet at a temperature below themold temperature, thus retaining the molded forms in the desired shape.As a further alternative, hot melt remoistenable adhesive may be applieddirectly to the molded sheet as it leaves the molding station. Further,double-gummed tapes may be ironed onto the sheet of molded felt, orpressure-sensitive mass can be solvent spread or transferred onto thefelt. If desired, a double faced pressuresensitive tape can be anchoredto the article, the one mass designed to adhere to the felt, and theother to the skin or shoe.

It will be apparent that pads of the present invention may be used forother purposes in connection with the body than on the feet. The processand product of the invention are applicable to articles designed forcushioning effect, such as knee pads, shoulder pads, helmet liners, andsupporters of various kinds. Very special pads with tails or anchorstrips can be died and heat pressed into a permanently set form. Theadhesive surface, if such is elasticity, and abrasion resistance and isconstructed of felted staple fibers bonded together throughout the pad,said pad having uniform weight per unit area and its liber density beinginversely proportional to its thickness, said pad having edge portionsand central portions, the density ratio of said edge portions to saidcentral portions being at least 2:1, and the resiliency of said padbeing in the range of about 70 to 100%.

2. A body protective pad as of claim 1 wherein the fibermixture'includes 5 to 25% of heat-activated bonding fibers and the saidmixture is bonded together by heatsetting.

3. A foot pad of claim 2 constructed of heat-set staple i fiber of asynthetic polymer of the group consisting of polyacrylonitrile,polyethylene and a polyester'of polyvhydric alcohol and polybasie acid,and vhaving an adhesive layer secured to its bottom surface.

4. A body-protective pad of claim 3having maximum thickness in theapproximate range 0.05 to 0.25 inch and weight in the approximate range2.0 to 64 ounces per square yard.

5. A foot pad of claim 4 wherein the density ratii` at least 5:1.

References Cited in the tile of this patent UNITED STATES PATENTS1,288,225 schon Dec. 11, 191s 2,519,013 Banigan Aug. 15, 195o 2,521,984Lang sept. 12, 195o 2,616,128 Pinard Apr. 2o, 1954 FOREIGN rATEN'rs448,610 ormai-nain June 11. 1936

